1. Field of the Invention
This invention relates generally to semiconductor manufacture, and more particularly, to a method and apparatus for controlling wafer uniformity using spatially resolved sensors.
2. Description of the Related Art
In the manufacture of semiconductor devices, wafers, such as silicon wafers, are subjected to a number of processing steps. The processing steps include depositing or forming layers, patterning the layers, and removing portions of the layers to define features on the wafer. One such process step is the formation of a layer by chemical vapor deposition, where reactive gases are introduced into a vessel containing the semiconductor wafers. The reactive gases facilitate a chemical reaction that causes a layer to form on the wafers.
Commonly, variation in the thickness of the deposited layer exists across the wafer. For example, the thickness of the layer deposited on the periphery may be greater or less than the thickness of the layer deposited in the center of the wafer. Such thickness variations, if sufficiently large, may result in defects in the various die defined on the wafer. Thickness variation across the wafer also complicates subsequent processing of the wafer. For example, strip times or polish times are designed based on an assumed or designed thickness of the previously formed layers. If the thickness in a certain region is sufficiently less than the design thickness, an over-strip or over polish may occur, thus damaging the underlying topology.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
One aspect of the present invention is seen in a processing system including a sensor, a processing tool, and an automatic process controller. The sensor has a plurality of sensing regions. The processing tool is adapted to process at least one process layer on a wafer. The process tool includes a process control device controllable by a process control variable. The sensor is adapted to measure a process layer characteristic of the process layer in a selected one of the sensing regions. The automatic process controller is adapted to receive the process layer characteristics measured by the sensor and adjust the process control variable in response to the process layer characteristic measured in one sensing region differing from the process layer characteristic measured in another sensing region.
Another aspect of the present invention is seen in a method for controlling wafer uniformity. The method includes processing a process layer on a wafer; measuring a characteristic of the layer in a plurality of sensing locations; and changing a process control variable of a process control device in response to the process layer characteristic measured in one sensing location differing from the process layer characteristic measured in another sensing location to affect the rate of processing the process layer in at least one of the sensing locations.